What was found
AIR DIVERSION, HYD Y RESVOIR LOW LEVEL. IAW FLT CREW THEY SHUTOFF YELLOW HYD PUMP AND ENGINE PUMP. RESERVOIR NOT EMPTY. PUMPS DID NOT CAVITATE. FOUND ON YELLOW HP MANIFOLD. CAPPED OFF LINE, O-RING BAD, REPLACED O-RING IAW AMM 29-00-00, AND LEAK CHECKED IAW AMM 29-00-00, OPS AND LEAK CHECK OK. AIRCRAFT MAKE A UNEVENTFUL LANDING.